Ovenable coated paperboard

ABSTRACT

This invention relates to ovenable and dual-ovenable coated paperboard suitable for use in producing food trays. More particularly, the invention relates to paperboard substrates which have been coated with a water-based release coating composition. Food trays made from such paperboard have superior grease resistance, high temperature resistance, and excellent food release properties—characteristics which make these trays particularly suitable for use in baking applications.

This application is a continuation-in-part of our commonly assigned,U.S. patent application Ser. No. 09/135,945, filed Aug. 18, 1998, nowU.S. Pat. No. 6,103,802 entitled “Water-Based Release Coatings”.

FIELD OF INVENTION

This invention relates to ovenable and dual-ovenable coated paperboardsuitable for use in producing food trays. More particularly, theinvention relates to paperboard substrates which have been coated with awater-based release coating composition. Food trays made from suchpaperboard have superior grease resistance, high temperature resistance,and excellent food release properties—characteristics which make thesetrays particularly suitable for use in baking applications.

BACKGROUND OF THE INVENTION

It has become a common practice to package convenience foods indisposable cooking or heating utensils made of coated paperboard. Due tothe increased popularity of microwave cooking, substantial efforts havebeen made to provide dual-ovenable containers which are suitable forboth conventional oven and microwave oven cooking. Accordingly, a numberof polymeric plastic paperboard coatings have been developed to protectpaperboard containers and their contents from the temperature extremesassociated with cold storage and heating. For example, U.S. Pat. No.3,813,256 discloses food heating utensils made of paperboard coated withpolyphenylene oxide or polysulfones. The use of paperboard productscoated with polypropylene or polyester are disclosed in U.S. Pat. Nos.3,904,104 and 4,147,836. U.S. Pat. No. 4,421,825 discloses the use oftitanium dioxide in coatings to give the paperboard resistance tobrowning.

There is a growing market demand for disposable paperboard for use inbaking applications with food products such as cinnamon rolls, biscuits,and the like. However, these foods have proven to be difficult tosuccessfully package in that they have a tendency to stick to thepaperboard when baked. As sugar tends to caramelize upon heating, thisadherence problem is particularly pronounced in those cases where thepackaged food contains high levels of sugar.

Dual-ovenable food trays are disclosed in U.S. Pat. No. 5,494,716; whileU.S. Pat. No. 5,002,833 discloses polymethylpentene (PMP)extusion-coated paperboard of the type currently utilized for ovenablebaking applications. Although PMP paperboard can exhibit good greaseresistance, heat resistance, and food release characteristics, the highmaterial and processing costs associated with PMP paperboard makes thistype of coated paperboard relatively expensive to use. Moreover, PMPpaperboard may prove to be somewhat difficult to recycle.

Therefore, an object of this invention is to provide ovenable paperboardsuitable for use in producing food trays for baking applications.

A further object of this invention is to solve the baking productadherence problem by providing ovenable coated paperboard which exhibitsgood grease resistance, high heat resistance and good food releasecharacteristics.

Yet another object of this invention is to provide a dual-ovenable foodtray coated with an aqueous coating composition that performs withoutgrease seepage, browning, and emission of odors during cooking.

Additional objects, advantages, and novel features of the invention willbe set forth in part in the description which follows.

SUMMARY OF THE INVENTION

These and other objects of the invention, as embodied and broadlydescribed herein, are met by coating a paperboard substrate with anaqueous coating composition comprising at least one styrene-acryliclatex copolymer, a stearate, and, optionally, silicone.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to ovenable and dual-ovenable coatedpaperboard having good grease resistance, high heat resistance and goodfood release characteristics. More particularly, the present inventionrelates to an aqueous coating composition and its use in the fabricationof ovenable and dual-ovenable food trays. The aqueous coatingcomposition may be applied to any conventional substrate, but preferablyto a paperboard substrate. The aqueous coating composition may also beapplied to the surface of other coatings.

Ovenable and dual-ovenable food trays suitable for use in the presentinvention comprise a paperboard substrate which is coated on at leastone side thereof with an aqueous coating composition comprising:

A) from about 20 to about 50 wt. % (based on the total weight of thesolids in the coating composition or BOS) of a member selected from thegroup consisting of the styrene-acrylic latex copolymer additionpolymerization reaction products of

1) from about 60 to about 90 wt. % (based on the total weight of thepolymer or BOP) of at least one nonionic free radical polymerizablemonomer,

2) up to about 5 wt. % BOP of at least one acidic free radicalpolymerizable monomer, and

3) from about 40 to about 10 wt. % BOP of at least one alkali-solublestabilizing resin having an acid number of at least 150 mg KOH/g,wherein said reaction products have a glass transition temperature inthe range of from about −40° C. to about 10° C., and combinationsthereof;

B) from about 80 to about 50 wt. % BOS of a member selected from thegroup consisting of calcium stearate, zinc stearate, and combinationsthereof;

C) up to about 5 wt. % BOS of silicone; and

D) water.

Preferred aqueous coating compositions suitable for use in the presentinvention comprise those having:

A) from about 20 to about 50 wt. % BOS of a member selected from thegroup consisting of the styrene-acrylic latex copolymer additionpolymerization reaction products of

1) from about 70 to about 80 wt. % BOP of at least one nonionic freeradical polymerizable monomer,

2) up to about 5 wt. % BOP of at least one acidic free radicalpolymerizable monomer, and

3) from about 30 to about 20 wt. % BOP of at least one alkali-solublestabilizing resin having an acid number of at least 150 mg KOH/g,wherein said reaction products have a glass transition temperature inthe range of from about −40° C. to about 10° C., and combinationsthereof;

B) from about 80 to about 50 wt. % BOS of a member selected from thegroup consisting of calcium stearate, zinc stearate, and combinationsthereof;

C) up to about 5 wt. % BOS of silicone; and

D) water.

If desired, the aqueous coating compositions may contain one or moreadjuvants for improving the physical and/or mechanical properties of thefood trays on which the compositions are applied. Suitable adjuvantsinclude, for example, thickening agents, coalescent solvents (such aspolyols), defoaming/dispersing agents, and agents for improving otherproperties of the coated food trays. Other additives (such as aqueousammonia) can be added to adjust the pH of the coating compositions.

The aqueous coating composition may also be employed as the top coatingor food contact layer on multi-layer coated paperboard. That is, one ormore coatings may be layered between the paperboard substrate and thepresent aqueous coating composition to impart desired characteristics tothe food tray.

The styrene-acrylic latex copolymer should have a glass transitiontemperature (T_(g)) of between about −40° C. and about 10° C.; with thepreferred T_(g) range being between about −20° C. and about 5° C.

Monomers which are suitable for use in the present invention includeethylenically unsaturated monomers such as olefins, monovinylaromatics,alpha, beta-ethylenically unsaturated carboxylic acids and estersthereof, ethylenically unsaturated dicarboxylic anhydrides (or acids)and esters thereof, and halo substituted olefmics. Specific examples ofthese monomers include, but are not limited to, the following: styrene,alpha-methylstyrene, acrylic acid, methacrylic acid, methylmethacrylate, butyl methacrylate, butyl acrylate, 2-ethylhexl acrylate,ethyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate,isobutyl methacrylate, itaconic acid, and combinations thereof. It isfurther preferred that the styrene-acrylic latex copolymer containnonionic (meth)acrylate monomers. It is also further preferred that thealkali-soluble stabilizing resin be a styrene/maleic anhydridecopolymer.

Addition polymerization reactions are well-known to those skilled in theart. The type of free-radical polymerization initiator suitable for usein the addition polymerization reaction to produce the styrene-acryliclatex copolymer is known in the art to depend upon the desiredtemperature for the reaction. Suitable initiators include, but are notlimited to, the following: t-butyl peroxide, t-butyl peroxybenzoate,t-butyl peroctoate, cumene hydroperoxide, azobisisobutyronitrile,benzoyl peroxide, ammonium persulfate and combinations thereof.

The pH at which the styrene-acrylic latex copolymers are prepared mayaffect their stability. The preferred pH range for use in the additionpolymerization reaction is from about 7.0 to about 11.0, with the mostpreferred pH range being about 8.0 to about 9.5.

It is further preferred to utilize a calcium stearate dispersion toproduce the aqueous coating composition.

The coating composition may be applied to a food tray substrate, such asa paperboard substrate, in any manner known in the art. Suitableapplication methods include the use of blades, air knifes, rod coatersand the like. The coating composition may be applied to either or bothsides of the substrate.

The following examples are provided to further illustrate the presentinvention and are not to be construed as limiting the invention in anymanner.

EXAMPLE 1

A 1000 ml resin kettle was charged with 18.3 g of SMA 1000 (a 1:1styrene:maleic anhydride (SMA) copolymer from Elf-Atochem), 12.0 g ofSMA 2000 (a 2:1 SMA copolymer from Elf-Atochem), 12.0 g of SMA 3000 (a3:1 SMA copolymer from Elf-Atochem), 12.0 g CA-897 (an emulsionpolymerization surfactant stabilizer from Rhone-Poulenc), 6.8 g ofammonium hydroxide, and 360.0 g of deionized water and heated to 82° C.After the resin was completely dissolved (approximately 1.5 hrs.), thepH of the initial charge was measured and adjusted to 8.5. A solution of2.25 g of ammonium persulfate in 10.0 g of water was added to thereactor, and a monomer mixture of 116.0 g of methylmethacrylate and141.7 g of 2-ethylhexacrylate was added continuously over a 2 hourperiod. After the feeds were complete, the reaction was held for 30minutes and an additional charge of 1.8 g of ammonium persulfate in 10.0g of water was added to convert any residual monomers. Subsequently,77.5 g of a zinc ammonium carbonate solution (consisting of 5.1 g ofzinc oxide, 6.3 g of ammonium carbonate, 14.2 g of ammonium hydroxide,and 51.9 g of water) was added over a period of 30 minutes, and theresult was filtered on a 325-mesh screen. The resulting final product(hereinafter referred to as Polymer No. 1) had a non-volatile content of40.85%, a pH of 9.6, and a T_(g) of −2.9° C.

A second polymer was produced by charging a 1000 ml resin kettle with95.9 g of SMA 1000 (a 1:1 SMA copolymer from Elf-Atochem), 4.1 g ofTL-70, a sulfonated polystyrene from National Starch, 25.4 g of ammoniumhydroxide, and 376.8 g of deionized water and heated to 82° C. After theresin was completely dissolved (approximately 1.5 hrs.), the pH of theinitial charge was measured and adjusted to 8.5. A solution of 2.25 g ofammonium persulfate in 10.0 g of water was added to the reactor, and amonomer mixture of 105.4 g of methylmethacrylate and 129.5 g of2-ethylhexacrylate was added continuously over a 2 hour period. Afterthe feeds were complete, the reaction was held for 30 minutes and anadditional charge of 1.8 g of ammonium persulfate in 10.0 g of water wasadded to convert any residual monomers. Subsequently, 60.0 g of a zincammonium carbonate solution (consisting of 7.0 g of zinc oxide, 8.5 g ofammonium carbonate, 14.4 g of ammonium hydroxide, and 60.0 g of water)was added over a period of 30 minutes, and the result was filtered on a325-mesh screen. The resulting final product (hereinafter referred to asPolymer No. 2) had a non-volatile content of 47.20%, a pH of 8.5, and aT_(g) of −2.9° C.

A third polymer was produced by charging a 1000 ml resin kettle with69.6 g of SMA 1000 (a 1:1 SMA copolymer from Elf-Atochem), 22.0 g ofammonium hydroxide, and 314.7 g of deionized water and heated to 84° C.After the resin was completely dissolved (approximately 1.5 hrs.), thepH of the initial charge was measured and adjusted to 8.5. Subsequently,0.64 g of ammonium persulfate in 3.2 g of water and cumene hydroperoxidewere added to the reactor, and the monomer mixture of 116.0 g ofmethylmethacrylate and 141.7 g of 2-ethylhexacrylate was addedcontinuously over a 2 hour period. A co-feed consisting of 1.27 g ofammonium persulfate in 38.2 g of water was also added to maintain highconversion while reducing grit formation. After the feeds were complete,the reaction was held for 30 minutes and an additional charge of 0.5 gof ammonium persulfate in 14.2 g of water was added to convert anyresidual monomers. The final product was filtered and 0.16 grams wereretained on a 325-mesh screen. The final product (hereinafter referredto as Polymer No. 3) had a non-volatile content of 44.8%, a pH of 8.4, aBrookfield viscosity of 75 cps (#4 at 100 rpm, 22° C.), and a T_(g) of−2.9° C.

A series of water-based release coating compositions were produced byemploying either Polymer No. 1, 2, or 3 in combination with calciumstearate and, where desired, silicone (see Table 1 below). The desiredpolymer was charged to a clean 2 L flask equipped with a stirrer and thecalcium stearate and/or silicone was added to the polymer with stirring.The mixture was stirred for ten minutes, then allowed to settle.

A series of ovenable food trays were produced by applying theabove-noted coating compositions with a Number 7 rod to the felt side ofstandard 18 pt. paperboard (C1S PRINTKOTE®, manufactured by WestvacoCorporation). The coatings were subsequently dried in a convection ovenat 105° C. for 30 seconds, then allowed to cool. A number ofsugar-containing cinnamon rolls were then placed on the coated side ofthe paperboard food trays and inserted into a convection oven (which hadbeen preheated to a temperature of 375° F.) for a period of about 10 to15 minutes. Thereafter the food trays and rolls were removed from theoven and allowed to cool for 1 minute prior to tilting the food trays toaround a 60° angle to remove the rolls from the food trays. Theevaluation results are given in Table 1 below.

TABLE 1 Release Properties, Heat Resistance, and Grease Resistance ofOne Layer Coatings Calcium Polymer Stearate Sili- Coat- Wt. Wt. cone³Resistance⁴ Percent ing No. %¹ Type² % % Grease Heat Released⁵ A. 1 48.71 48.8 2.5 3.5 4.5 95% B. 1 44.0 1 55.0 1.0 3.5 4.5 95% C. 1 44.7 1 55.30.0 3.5 4.5 75% D. 2 30.0 3 60.0 0.0 4.0 3.5 95% E. 3 50.0 2 50.0 0.03.5 4.5 90% F. 3 40.0 2 60.0 0.0 4.5 4.5 80% G. 3 30.0 2 70.0 0.0 4.04.0 85% ¹Weight percent (Wt. %) is based upon the total weight of thecoating. ²1: Ferro (a calcium stearate dispersion from Grant Chemical).2: FLOWCO 53 (a calcium stearate dispersion from Henkel Corporation). 3:LUBRICAL 48 (a calcium stearate dispersion from Witco, Inc.) ³SILICONE175 (a silicone additive from Dow Corning ® 175 Additive). ⁴Resistanceto grease and heat was measured on a 1-5 scale, with 5 indicatingexcellent resistance and 1 indicating extremely poor resistance.⁵Percent released refers to the percent of the portion of the roll incontact with the paperboard which freely released.

As noted above, the coated paperboard food trays not only exhibitedsuperior resistance to both grease and heat, but they also showedexcellent food release properties (even when employed with bakingproducts containing a high sugar content).

EXAMPLE 2

A chemical reactor was charged with 159 parts water and 35 parts SMA1000 (a 1:1 SMA copolymer from Elf-Atochem), and the reactor was heatedup to the reaction temperature of 82° C. About 11 parts ammoniumhydroxide was added to the mixture when the reactor reached 35-40° C.The heat of neutralization produced an exothermic response which raisedthe temperature of the reactor to about 65° C. Once the reactor reached82° C., the reaction was held for 3-4 hours until the SMA resin wascompletely dissolved. After the resin had dissolved, a solution of 1part ammonium persulfate in 38 parts water and a monomer mixture of 58parts methylmethacrylate and 71 parts 2-ethylhexacrylate were co-fed andcontinuously added over a two-hour period. The reaction temperature wasmaintained at 83 ±1° C. After the feeds were complete, the reaction washeld for 30 minutes and a solution of 1 part ammonium persulfate in 30parts water was added. The reaction was held for one hour to completethe monomer conversion. The reaction was cooled and filtered with a200-mesh screen. The final polymer product had a non-volatile content ofabout 45%, a pH of 8.4, a Brookfield viscosity of 75 cps (#4 at 100 rpm,22° C.), and a T_(g) of −23.6° C.

A water-based release coating composition was produced by mixing 30parts of the polymer with 70 parts of FLOWCO 53 (a calcium stearatedispersion from Henkel Corporation) for about 20 minutes. The resultingcoating composition was subsequently utilized to produce dual-ovenablepaperboard by coating 16 pt. paperboard (PRINTKOTE®, manufactured byWestvaco Corporation) using a number 5 rod at press speeds from 200 to500 ft/min. Samples from the run were employed to produce a series offood trays, which were evaluated for grease resistance, heat resistance,and release properties of baked cinnamon rolls using the methoddescribed in Example 1. The results are shown in Table 2 below.

TABLE 2 Evaluation of Grease Resistance, Heat Resistance and ReleaseProperties Sample Grease Resistance¹ Heat Resistance¹ Release² (%) 1 4.04.8 100 100 2 4.0 4.8 90 90 3 4.5 4.8 90 85 4 4.0 4.8 85 100 Average 4.14.8 91 ¹Resistance to grease and heat was measured on a 1-5 scale, with5 indicating excellent resistance and 1 indicating extremely poorresistance. ²Percent released refers to the percent of the portion ofthe roll in contact with the paperboard which freely released.

The data in Table 2 show that the coated paperboard food trays exhibitedsuperior grease resistance, heat resistance, and release properties.

EXAMPLE 3

A polymer for use in producing the release coating compositions suitablefor employment in the present invention was produced via the followingmethod. A 1000 ml resin kettle was charged with 30.0 g of SMA 2000 (a2:1 styrene:maleic anhydride (SMA) copolymer from Elf-Atochem), 24.0 gCA-897 (an emulsion polymerization surfactant stabilizer fromRhone-Poulence), 13.2 g of ammonium hydroxide, and 300.0 g of deionizedwater and heated to 82° C. After the resin was completely dissolved(approximately 1.5 hrs.), the pH of the initial charge was measured andadjusted to 8.5. A solution of 2.25 g of ammonium persulfate in 10.0 gof water was added to the reactor, and a monomer mixture of 123.0 g ofmethylnethacrylate and 123.0 g of 2-ethylhexacrylate was addedcontinuously over a 2 hour period. After the feeds were complete, thereaction was held for 30 minutes and an additional charge of 1.8 g ofammonium persulfate in 10.0 g of water was added to convert any residualmonomers. Subsequently, 56.0 g of a zinc ammonium carbonate solution(consisting of 25.0 g of zinc oxide, 30.0 g of ammonium carbonate, 50.0g of ammonium hydroxide, and 80.0 g of water) was added over a period of30 minutes, and the result was filtered on a 325-mesh screen. Theresulting final product (hereinafter referred to as Polymer No. 4) had anon-volatile content of 40.85%, a pH of 9.6, and a T_(g) of 4.3° C.

A second polymer suitable for employment in the present invention wasproduced via the following method. A 1000 ml resin kettle was chargedwith 80.2 g of SMA 1000 (a 1:1 SMA copolymer from Elf-Atochem), 3.4 g ofTL-70, a sulfonated polystyrene from National Starch, 20.5 g of ammoniumhydroxide, and 371.5 g of deionized water and heated to 82° C. After theresin was completely dissolved (approximately 1.5 hrs.), the pH of theinitial charge was measured and adjusted to 8.5. A solution of 2.25 g ofammonium persulfate in 10.0 g of water was added to the reactor, and amonomer mixture of 105.3 g of methylmethacrylate and 130.3 g of2-ethylhexacrylate was added continuously over a 2 hour period. Afterthe feeds were complete, the reaction was held for 30 minutes and anadditional charge of 1.8 g of ammonium persulfate in 10.0 g of water wasadded to convert any residual monomers. Subsequently, 60.0 g of a zincammonium carbonate solution (consisting of 7.4 g of zinc oxide, 8.5 g ofammonium carbonate, 7.0 g of ammonium hydroxide, and 60.6 g of water)was added over a period of 30 minutes, and the resulting final product(hereinafter referred to as Polymer No. 5) was filtered on a 325-meshscreen and a T_(g) of −2.9° C.

A water-based release coating composition was produced using Polymer No.4, calcium stearate, and silicone Dow Corning® 175 Additive (see Table 2below). The polymer was charged to a clean 2 L flask equipped with astirrer and the calcium stearate and silicone was added to the polymerwith stirring. The mixture was stirred for ten minutes, then allowed tosettle.

A first polymer was drawn down with a Number 7 rod on the felt side ofstandard 18 pt. paperboard (C1S PRINTKOTE®, manufactured by WestvacoCorporation). The coated paperboard was dried in a convection oven at105° C. for 30 seconds and allowed to cool. Thereafter a release coatingcomposition was applied with a Number 7 rod on top of the first polymeras the food contact layer. For comparison purposes, a control food traywas produced using a hundred percent silicone solution drawn down on topof the polymer as the food contact layer (Example 3 below). The coatedpaperboard was subsequently dried in a convection oven at 105° C. for 30seconds and allowed to cool.

A number of sugar-containing cinnamon rolls were placed on the coatedside of the paperboard and inserted into a convection oven (which hadbeen preheated to a temperature of 375° F.) for a period of from 10 to15 minutes. The paperboard and rolls were then removed from the oven andallowed to cool for 1 minute prior to removal of the rolls from theboard. The results of the evaluations are given in Table 3 below.

TABLE 3 Release Properties, Heat, and Grease Resistance of Two LayerCoatings First Layer Second Layer (Top) Coating Composition (Bottom)Calcium Polymer Polymer Stearate Silicone³ Resistance⁴ Percent ExampleNo. No. Wt. %¹ No.² Wt. % Wt. % Grease Heat Released⁵ 1. 1 4 48.5 1 48.53.0 5 4 95 2. 4 4 48.5 2 48.5 3.0 5 4.5 98  3.⁶ 5 N/A 0.0 N/A 0.0 100.05 3 50 ¹Weight percent (Wt. %) is based upon the total weight of thecoating. ²1: FERRO (a calcium stearate dispersion from Grant Chemical).2: FLOWCO 53 (a calcium stearate dispersion from Henkel Corporation).³Silicone Dow Corning ® 175 Additive (a silicone additive from DowCorning). ⁴Resistance to grease and heat was measured on a 1-5 scale,with 5 indicating excellent resistance and 1 indicating extremely poorresistance. ⁵Percent released refers to the percent of the portion ofthe roll in contact with the paperboard which was freely released.⁶Example used as a control.

As shown above, the two-layer coated paperboards exhibited superiorgrease resistance, heat resistance, and release properties. Thesefavorable characteristics are particularly evident when compared thecontrol paperboard (which had a top layer of silicone).

EXAMPLE 4

A polymer suitable for use in producing the present invention wasproduced via the following method. A 1000 ml resin kettle was chargedwith 30.0 g of SMA 2000 (a 2:1 styrene:maleic anhydride (SMA) copolymerfrom Elf-Atochem), 24.0 g CA-897 (an emulsion polymerization surfactantstabilizer from Rhone-Poulenc), 13.2 g of ammonium hydroxide, and 300.0g of deionized water and heated to 82° C. After the resin was completelydissolved (approximately 1.5 hrs.), the pH of the initial charge wasmeasured and adjusted to 8.5. A solution of 2.25 g of ammoniumpersulfate in 10.0 g of water was added to the reactor, and a monomermixture of 123.0 g of methylmethacrylate and 123.0 g of2-ethylhexacrylate was added continuously over a 2 hour period. Afterthe feeds were complete, the reaction was held for 30 minutes and anadditional charge of 1.8 g of ammonium persulfate in 10.0 g of water wasadded to convert any residual monomers. Subsequently, 56.0 g of a zincammonium carbonate solution (consisting of 25.0 g of zinc oxide, 30.0 gof ammonium carbonate, 50.0 g of ammonium hydroxide, and 80.0 g ofwater) was added over a period of 30 minutes, and the result wasfiltered on a 325-mesh screen. The resulting polymer product had anon-volatile content of 40.85%, a pH of 9.6, and a T_(g) of 4.3° C.

A water-based release coating composition was produced by charging 6.0 gof the polymer to a clean 2 L flask equipped with a stirrer.Subsequently, 14.0 g of LIQUAZINC AQ-90 (a zinc stearate solution fromWitco Corporation) was added to the polymer with stirring. The mixturewas stirred for ten minutes, then allowed to settle. The resultingcoating composition was applied with a Number 7 rod to the felt side ofstandard 18 pt. paperboard (C1S PRINTKOTE®, manufactured by WestvacoCorporation). The coated food tray was dried in a convection oven at105° C. for 30 seconds, then allowed to cool. A number ofsugar-containing cinnamon rolls were then placed on the coated side ofthe paperboard food tray and inserted into a convection oven (which hadbeen preheated to a temperature of 375° F.) for a period of about 10 to15 minutes. Thereafter the food tray and rolls were removed from theoven and allowed to cool for 1 minute prior to tilting the paperboard toremove the rolls. Using the evaluation method described in Example 1,the coated paperboard had a grease resistance of 5, a heat resistance of3, and a release percentage of 80.

Many modifications and variations of the present invention will beapparent to one of ordinary skill in the art in light of the aboveteachings. It is therefore understood that the scope of the invention isnot to be limited by the foregoing description, but rather is to bedefined by the claims appended hereto.

What is claimed is:
 1. An ovenable food tray comprising a paperboardsubstrate which is coated on at least one side thereof with an aqueouscoating composition comprising: A) from about 20 to about 50 wt. % BOSof a member selected from the group consisting of the styrene-acryliclatex copolymer addition polymerization reaction products of 1) fromabout 60 to about 90 wt. % BOP of at least one nonionic free radicalpolymerizable monomer, 2) up to about 5 wt. % BOP of at least one acidicfree radical polymerizable monomer, and 3) from about 46 to about 10 wt.% BOP of at least one alkali-soluble stabilizing resin having an acidnumber of at least 150 mg KOH/g, wherein said reaction products have aglass transition temperature in the range of from about −40° C. to about10° C., and combinations thereof; B) from about 80 to about 50 wt. % BOSof a member selected from the group consisting of calcium stearate, zincstearate, and combinations thereof; C) up to about 5 wt. % BOS ofsilicone; and D) water.
 2. The ovenable food tray of claim 1, whereinthe aqueous coating composition further comprises: A) from about 20 toabout 50 wt. % BOS of a member selected from the group consisting of thestyrene-acrylic latex copolymer addition polymerization reactionproducts of 1) from about 70 to about 80 wt. % BOP of at least onenonionic free radical polymerizable monomer, 2) up to about 5 wt. % BOPof at least one acidic free radical polymerizable monomer, and 3) fromabout 30 to about 20 wt. % BOP of at least one alkali-solublestabilizing resin having an acid number of at least 150 mg KOH/g,wherein said reaction products have a glass transition temperature inthe range of from about −40° C. to about 10° C., and combinationsthereof; B) from about 80 to about 50 wt. % BOS of a member selectedfrom the group consisting of calcium stearate, zinc stearate, andcombinations thereof; C) up to about 5 wt. % BOS of silicone; and D)water.
 3. The ovenable food tray of claim 1 wherein the styrene-acryliclatex copolymer has a glass transition temperature of between about −20°C. and about 5° C.
 4. The ovenable food tray of claim 1 wherein themonomer is an ethylenically unsaturated monomer selected from the groupconsisting of olefms, monovinylaromatics, alpha, beta-ethylenicallyunsaturated carboxylic acids and esters thereof, ethylenicallyunsaturated dicarboxylic anhydrides and esters thereof, ethylenicallyunsaturated dicarboxylic acids and ester thereof, halo substitutedolefinics, and combinations thereof.
 5. The ethylenically unsaturatedmonomer of claim 4 wherein the monomer is a member selected from thegroup consisting of styrene, alpha-methylstyrene, acrylic acid,methacrylic acid, methyl methacrylate, butyl methacrylate, butylacrylate, 2-ethylhexyl acrylate, ethyl acrylate, hydroxyethyl acrylate,hydroxyethyl methacrylate, isobutyl methacrylate, itaconic acid, andcombinations thereof.
 6. The ovenable food tray of claim 1 wherein thepaperboard substrate is coated on at least one side thereof with atleast two coating layers of which the top coating layer is the aqueouscoating composition of claim
 1. 7. A duel-ovenable food tray comprisinga paperboard substrate which is coated on at least one side thereof withan aqueous coating composition comprising: A) from about 20 to about 50wt. % BOS of a member selected from the group consisting of thestyrene-acrylic latex copolymer addition polymerization reactionproducts of 1) from about 60 to about 90 wt. % BOP of at least onenonionic free radical polymerizable monomer, 2) up to about 5 wt. % BOPof at least one acidic free radical polymerizable monomer, and 3) fromabout 40 to about 10 wt. % BOP of at least one alkali-solublestabilizing resin having an acid number of at least 150 mg KOH/g,wherein said reaction products have a glass transition temperature inthe range of from about −40° C. to about 10° C., and combinationsthereof; B) from about 80 to about 50 wt. % BOS of a member selectedfrom the group consisting of calcium stearate, zinc stearate, andcombinations thereof; C) up to about 5 wt. % BOS of silicone; and D)water.
 8. The dual-ovenable food tray of claim 7, wherein the aqueouscoating composition further comprises: A) from about 20 to about 50 wt.% BOS of a member selected from the group consisting of thestyrene-acrylic latex copolymer addition polymerization reactionproducts of 1) from about 70 to about 80 wt. % BOP of at least onenonionic free radical polymerizable monomer, 2) up to about 5 wt. % BOPof at least one acidic free radical polymerizable monomer, and 3) fromabout 30 to about 20 wt. % BOP of at least one alkali-solublestabilizing resin having an acid number of at least 150 mg KOH/g,wherein said reaction products have a glass transition temperature inthe range of from about −40° C. to about 10° C., and combinationsthereof, B) from about 80 to about 50 wt. % BOS of a member selectedfrom the group consisting of calcium stearate, zinc stearate, andcombinations thereof; C) up to about 5 wt. % BOS of silicone; and D)water.
 9. The dual-ovenable food tray of claim 7 wherein thestyrene-acrylic latex copolymer has a glass transition temperature ofbetween about −20° C. and about 5° C.
 10. The dual-ovenable food tray ofclaim 7 wherein the monomer is an ethylenically unsaturated monomerselected from the group consisting of olefins, monovinylaromatics,alpha, beta-ethylenically unsaturated carboxylic acids and estersthereof, ethylenically unsaturated dicarboxylic anhydrides and estersthereof, ethylenically unsaturated dicarboxylic acids and ester thereof,halo substituted olefinics, and combinations thereof.
 11. Theethylenically unsaturated monomer of claim 10 wherein the monomer is amember selected from the group consisting of styrene,alpha-methylstyrene, acrylic acid, methacrylic acid, methylmethacrylate, butyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate,ethyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate,isobutyl methacrylate, itaconic acid, and combinations thereof.
 12. Thedual-ovenable food tray of claim 7 wherein the paperboard substrate iscoated on at least one side thereof with at least two coating layers ofwhich the top coating layer is the aqueous coating composition of claim1.